GELLAB is an exploratory data analysis system for the analysis of sets of 2D electrophoretic gel images. GELLAB incorporates sophisticated subsystems for image acquisition and processing, database manipulation and graphics as well as statistical analysis. It has been applied to a variety of experimental systems in which quantitative and qualitative changes in one or more proteins among hundreds or thousands of unaltered proteins is the basic analytic problem. Keeping track of changes detected using these methods is also a major attribute of the system. A composite gel database may be "viewed" under different exploratory data analysis conditions and statistical differences and subtle patterns elucidated from "slices" of an effectively 3D database. Results can be presented in a variety of tables, plots or derived images. The computer workstation based system, GELLAB-II, now runs under UNIX and uses X-windows for portable interactive graphics. Substantive applications include: analyzing sets of lymphocyte gels and long term cell lines from human hematological malignancies to identify potential marker proteins for possible microsequencing using a gas-phase sequenator (Lester); axonal proteins synthesized during axonal regeneration (Sonderegger); cadmium toxicity of epithelial cells (Sonderegger and Hunziker); cerebral endothelial cell morphology control (Bauer and Amberger); assess stability of long term cell lines (Alley).